Methods and apparatuses for monitoring a radio link

ABSTRACT

A method for monitoring a radio link between a base station and a terminal in a wireless communication system includes adapting at least one parameter, which is used in monitoring the radio link, based on a duration of an inactive phase in which the terminal is not transmitting to and/or receiving data from the base station via the radio link.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 35 U.S.C. § 371 national stage application of PCTInternational Application No. PCT/EP2015/062861, filed on Jun. 9, 2015,the disclosure and content of which is incorporated by reference hereinin its entirety.

TECHNICAL FIELD

The present invention relates to the field of radio link monitoring in awireless communication system, such as a cellular network, and, moreparticularly, to a method and a terminal for monitoring a radio linkfailure between the terminal and a base station (e.g. a serving basestation) in a wireless communication system, such as a cellular network.A terminal capable of monitoring a radio link and a base station forenabling a terminal to monitor a radio link as well as computer programsare also described herein.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) is responsible for thestandardization of the UMTS (Universal Mobile Telecommunication Service)system and LTE (Long term Evolution). LTE is a technology for realizinghigh-speed packet-based communication that can reach data rates of about100 Mbps on the downlink and about 50 Mbps on the uplink. The basestation in LTE, also known as eNB (enhanced Node B) or eNodeB, performsthe functions of a conventional radio access network (RNC) node and of aUMTS Node B. In addition, eNodeBs in LTE may interact directly with thecore network and with other eNodeBs.

Irrespective of the wireless or mobile communication system used, radiolink monitoring is vital to maintain radio connections. By regularlyreporting the radio conditions, different types of actions can be takenwhen radio link failures occur. In e.g. UTRA (UMTS Terrestrial RadioAccess Network), the physical layers estimate the quality of the radiolinks and report, on radio frame basis, the synchronization status tohigher layers. The synchronization status are reported via so calledsynchronization primitives which are described in greater details in thetechnical specification 3GPP TS 25.214 V12.2.0 titled: “Physical LayerProcedures (FDD)”.

The mechanism of reporting radio link quality status is also specifiedin E-UTRA (Evolved UTRA), in which a fast and reliable detection ofradio problems is considered essential in order to avoid unnecessaryinterference in uplink, waste of resources in downlink and unnecessarilylong delays before e.g. cell reselection or handover of a terminal cantake place.

The radio link failure handling in E-UTRA is described in the technicalspecifications 3GPP TS 36.300 V12.5.0 titled: “E-UTRA and EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) Overalldescription; Stage 2”. The handling of radio link failures described inthese specifications consists of two phases as illustrated in FIG. 2a .As shown, the first phase is started upon radio problem detection whichmay lead to radio link failure detection e.g. after a timer period hasexpired (the timer is denoted T310 in FIG. 1). In this first phase, usermobility is still controlled and managed by the network. This means thenetwork may perform a handover.

As also shown in FIG. 2a , the second phase is started upon radio linkfailure detection which may lead to a so called radio resource control(RRC) state transition from a connected mode, i.e. RRC_CONNECTED, to anidle mode, i.e. RRC_IDLE, after the expiry of e.g. a timer, denoted T311in FIG. 2a . In this second phase, the network loses control over theterminal. Therefore the terminal autonomously may take mobility relateddecisions in accordance with the specified terminal behavior, cf.section 10.1.6 of above mentioned TS 36.300 V12.5.0.

As mentioned earlier, the judgment (and reporting) of radio problemdetection, as well as procedures for its reporting, is handled by thephysical layer. The analogy with UTRA refers to the use of thepreviously mentioned synchronization primitives, e.g. the out ofsynchronization (out-of-sync) handling.

As an example, for E-UTRA downlink, the terminal monitors radio linkquality of the serving base station (or serving cell), in RRC connected(RRC_CONNECTED) mode, in order to indicate radio problems to higherlayers. If the terminal is not operating in a so called discontinuousreception mode (DRX mode), the physical layer in the terminal checks, inevery frame, the quality of the radio link measured over certainevaluation duration (e.g. 100 ms or 200 ms or any other suitable value)and compares against defined thresholds denoted Qin and Qout. When theradio quality determined by the terminal is worse (or less) than thethreshold Qout, the terminal indicates radio problem or the so calledout of synchronization to higher layers. The terminal continuesindicating radio problems until the quality becomes better than thethreshold Qin. It is the higher layer(s) that triggers the start andstop of monitoring i.e. radio problem detection.

In addition to the above mentioned thresholds used to detect radio linkproblems, there are additional so called higher layer filteringparameters that can be used in order to further increase the reliabilityof radio link failure detection especially for the cases where theterminal applies DRX and can avoid “ping-pong” betweenin-synchronization and out-of-sync. These parameters are known ashysteresis counters and timers. It should be noted that additionalparameters and coefficients can also be used, but typically timers andcounters are used. As an example, UTRA relies on timers and counters,denoted in 3GPP TS 25.331 V12.5.0 by N313 (Successive Out-Of-SyncReception Max) and N315 (Successive In-Sync Reception Counter). Theseare configured by higher layers i.e. via the network. They generallycount the number of out-of-sync and in-sync indications. For E-UTRA,higher layer filtering parameters such as timers and counters are e.g.described in the technical specification 3GPP TS 36.331 V12.5.0entitled: “E-UTRA Radio Resource Control (RRC); Protocol specification(Release 12)”. One of the timers mentioned in this technicalspecification and which relates to radio link failure detection andactions to be performed is denoted T310.

As mentioned before, the E-UTRA allows operation in DRX mode in RRCconnected mode. DRX is an ongoing work on the LTE network (i.e. onE-UTRAN), and is a mechanism defined to save battery time and resourcesof a terminal. With DRX a terminal can turn on and off reception oflayer 1/layer 2 (L1/L2) control in radio resource control connectedstate or connected mode, i.e. when the terminal has established an RRCconnection with the serving network.

In order to save battery time, the RRC connected mode terminal, whilebeing in sleep mode (‘OFF time’) during a predetermined DRX cycleperiod, wakes up at specific timings in order to check/monitor forpossible control channels allocated by the base station (e.g. eNB) todetermine if there is data to receive, the so called ‘ON time’. Whenthere is no data to receive, the terminal switches to the sleep mode andstays in the sleep mode until the next wake-up time. The control channelchecked/monitored by the terminal during the wake-up time is known asPDCCH (Physical Downlink Control Channel). When there is data toreceive, the terminal receives the data from the base station and sendsa response signal (ACK/NACK) indicating a success or a failure in thereception of the data transmitted. As an example, DRX uses one or twopredefined cycles (long and/or short cycles) at the beginning of whichthe terminal should monitor the PDCCH over a certain amount of TTIs(Transmission Time Interval) under a so called ‘ON time’. During the ‘ONtime’, the terminal monitors the PDCCH for PDCCH-subframe(s). The numberof consecutive PDCCH-subframe(s) at the beginning of the DRX cycle (i.e.during the Active Time) is known as the “On-duration Timer”. TheOn-duration timer in the beginning of each cycle also defines how long aterminal should monitor the PDCCH and is also based on the system framenumber (SFN), specified as an integer offset. The PDCCH can carry bothdownlink assignments as well as uplink grants scheduled by the basestation. It should be noted that the same DRX mechanism is used both forthe downlink (DL) and the uplink (UL).

Whether the terminal is awake (i.e. monitors the PDCCH) or is asleepafter the On-duration period depends on activity, i.e. possiblereceptions of PDCCH control data during that period. When the terminalsuccessfully decodes a PDCCH assignment or grant, it re(starts) the socalled inactivity timer. The inactivity timer extends the time duringwhich the terminal further monitors the PDCCH.

The DRX mode may be configured via higher layers (i.e. by RRC). Theterminal may thus be configured to use long DRX cycle or the short DRXcycle or both. The terminal always follows one DRX cycle at any momenteven if two DRX cycles (i.e. short and long DRX) are configured. Thenetwork (i.e. higher/upper layers) can configure a DRX cycle betweene.g. 2 ms and up to e.g. 2.56 seconds depending upon the type ofservice, e.g. 2-20 ms for voice over internet protocol (VoIP) and e.g.1-2 seconds for browsing on the Internet.

As mentioned before, when DRX is used, the terminal tries to stayinactive as much as possible during the silent periods of the DRX cycleto save its battery. However, this also implies that the terminal willmainly perform measurements at the wake up instances for e.g. mobilityreasons; radio link problem detection (e.g. out-of-sync detection andin-sync detection) etc.

A drawback with this is that due to the insufficient measurementopportunities in DRX mode (depending upon DRX cycle) it is possible thatthe terminal would be unable to promptly detect the radio link problem.

Furthermore, it is likely that a very large number of terminals are keptin DRX mode and the network can abruptly switch one or several terminalsto operate in continuous reception mode in order to transmit data. Thusthe terminal(s) should stay well connected in terms of radio linkquality and so any radio link problem(s) should be reported to thenetwork promptly. In other words, it is important that the radio linkproblem detection is designed to work effectively in both DRX andnon-DRX (i.e. continuous) modes of operation. But since the number ofmeasurements samples that are required to achieve estimation accuracyequivalent to non-DRX mode can be relatively large, a terminal operatingin DRX mode may fail to promptly detect radio link problems due to theinsufficient measurement opportunities (i.e. evaluation periods) by theterminal in DRX mode.

SUMMARY

It is thus an object of the invention to optimize power consumptionand—in case of a battery powered device—battery lifetime. It is afurther object of the invention to reduce the complexity of signalingand signaling overhead and thereby reduce energy consumption and/orextend battery lifetime even further. In particular in the framework ofmachine-type communication (MTC) it is an object of the invention toreduce the complexity of machine-type devices themselves, minimizesignaling overhead and extend—in case of battery powered machine typedevices—their battery lifetime even further. Another object of theinvention is to allow for extended DRX cycles as well as theimplementation of a power-saving mode (PSM) with a reduced wake-up time,especially for MTC devices.

According to a first embodiment of the present invention, the abovestated object is achieved by a method for monitoring a radio linkbetween a base station and a terminal in a wireless communicationsystem. The method may comprise: adapting at least one parameter, usedin monitoring said radio link, based on a duration of an inactive phase.In the inactive phase the terminal may not transmit to and/or receivedata from the base station via the radio link.

According to a second embodiment of the present invention, the abovestated object is achieved by a computer program comprising program code.The code may be executed by a processor of a terminal. By executing thecode the terminal may be configured to operate in accordance with amethod of the first embodiment.

According to a third embodiment of the present invention, the abovestated object is achieved by a terminal capable of monitoring a radiolink between the terminal and a base station. The terminal may beconfigured to adapt at least one parameter, used in monitoring saidradio link, based on a duration of an inactive phase. In the inactivephase the terminal may be configured not to transmit to and/or toreceive data from the base station via the radio link.

According to a fourth embodiment of the present invention the abovestated object is achieved by a base station for enabling a terminal tomonitor a radio link between the terminal and said base station. Theterminal may be configured not to transmit to and/or not to receive datafrom the base station via the radio link in an inactive phase. The basestation may be adapted to transmit a first message to the terminalsetting a predefined threshold. The predefined threshold may serve forcomparing predefined threshold or a parameter adapted accordingly with aduration of said inactive phase.

According to a fifth embodiment of the present invention the abovestated object is achieved by a method for use in a base station enablinga terminal to monitor a radio link between the terminal and said basestation. The method may comprise the steps of transmitting a message tothe terminal setting a predefined threshold for comparing saidpredefined threshold with a duration of an inactive phase. During theduration of the inactive phase the terminal may be configured not totransmit to and/or not to receive data from the base station via theradio link.

According to a sixth embodiment of the invention the object is achievedby a computer program comprising program code to be executed by aprocessor of a base station. By executing the code the terminal may beconfigured to operate in accordance with a method of the fifthembodiment.

An advantage of the embodiments of the present invention is thatreliable and especially fast radio problem detection is achieved evenwhen the terminal, which may very well be a machine-type-device (MTC),is operating in DRX mode and/or in a scenario with limited measurementopportunities. Further on it is a benefit of the present invention thatpower consumption of the terminal is reduced in case of a radio linkfailure and a subsequent re-establishment procedure.

Further objects and features of the embodiments of the present inventionwill become apparent from the following detailed description inconjunction with the accompanying drawings. The following drawings areillustrative only, and that various modifications and changes may bemade in the specific embodiments illustrated as described within thescope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a terminal moving through differentcells of a cellular network.

FIG. 2a shows a diagram illustrating an example of a scheme on how tohandle radio link failure.

FIG. 2b shows a diagram illustrating another example of a scheme on howto handle radio link failure.

FIG. 3 shows an exemplary flow chart schematically illustrating a methodaccording to an embodiment of the invention with regards to a terminal.

FIG. 4 shows a flow chart schematically illustrating a method accordingto an embodiment with regard to a base station.

FIG. 5 schematically illustrates exemplary structures for implementingan embodiment in a terminal.

FIG. 6 schematically illustrates exemplary structures for implementingan embodiment in a base station.

FIG. 7 schematically illustrates another flow chart diagram forimplementing an embodiment in a terminal.

FIG. 8 shows a diagram illustrating battery lifetime as a function ofDRX cycle length comparing the conventional method with the presentinvention.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, scenarios, techniques, etc. in order to provide athorough understanding of the exemplary embodiments of the presentinvention. However, it will be apparent for the person skilled in theart that the exemplary embodiments of the present invention may bepracticed in other embodiments that depart from these specific details.The different embodiments of the present invention are described hereinby way of reference to particular example scenarios. In particular theembodiments are described in a non-limiting general context in relationto a communications network based on the fourth generation (4G) LTEconcept. It should be noted that the embodiments of the presentinvention are not restricted to LTE but can be applicable in otherwireless systems that employ discontinuous reception (DRX) such as UMTS,WiMAX (worldwide interoperability for microwave access), or HSPA (highspeed packet access) or WCDMA (wideband code division multiple access)or HSDPA (high speed downlink packet access) or HSUPA (high speed uplinkpacket access) or other wireless communication techniques.

FIG. 1 schematically illustrates an embodiment in which a non-stationaryterminal 100 moves through different cells C1, C2, C3, C4 of a cellularnetwork. A terminal 100 may be any kind of wireless communication deviceas for example a user equipment (UE), a MTC-device, a mobile phone, asmartphone, a data modem, a mobile computer, or another kind of terminaldevice. The cellular network may be a network employed in accordancewith a specification of 3GPP. Although the cells are depicted in arectangular shape in FIG. 1, they may have arbitrary different shapes,for example hexagonal, circular etc.

Since the terminal 100 is non-stationary or portable it may be indifferent locations, e.g. P1-P4, at different points in time. Thereforethe terminal 100 may have to change between the different cells C1-C4.In normal operation, the terminal 100 has to be awake all the time andmonitor PDCCH for every subframe, meaning that it has to be awake allthe time since it doesn't know exactly when the network will transmitthe data, e.g. handover information or any other signaling. Thus theterminal 100 is capable of establishing a perpetual connected mode. Theperpetual connected mode may reduce the amount of signaling overheadrequired by the terminal (device) 100. However power consumption is highin such an operating mode. The terminal 100 may also be capable ofestablishing an extended discontinuous reception (DRX) cycle. Theextended DRX cycle may enable the terminal 100 to reduce energyconsumption while maintaining the perpetual connected mode. Remaining inRRC Connected mode or any type of (perpetual) connected mode hencecauses less signaling compared to going down to (RRC) Idle mode inbetween. Connected mode does not give less signaling in itself. Hencethe additional signaling is caused by moving from (RRC) idle mode to(RRC) connected mode. The (RRC) idle mode is enabled and/or accessiblewhen the terminal operates according to DRX, e.g. the terminal operatesin extended DRX mode.

During discontinuous reception (DRX) the terminal 100 may go into sleepmode for a certain period of time and wake up for another period oftime. The duration of a DRX cycle consists of an ‘ON time’ and an ‘OFFtime’. DRX provides a number of parameters, such as “onDurationTimer”,“drx-Inactivity timer” etc., which allow for adjusting of the differenttime intervals of DRX mode. In the present case, the ‘OFF time’ of a DRXcycle corresponds to an inactive phase of the terminal 100. However,other inactive phases, such as switching off the receiver and/ortransmitter unit RX, TX of the terminal 100 e.g. due to a power savingmode, extended DRX in idle mode, or when the device is switched off maybe available.

Keeping the terminal 100, e.g. a MTC device, constantly in RRC_CONNECTEDmode with extended DRX cycles is an ideal scenario to minimize both theRRC signaling overhead and terminal power consumption. This way, eveninfrequent data transmissions can be handled without any need forconnection setup signaling. However, due to the extended DRX cycles andin case the terminal 100 is not stationary, or the network conditionschange (e.g., due to HO parameter optimization, antenna tiltoptimization, power/interference optimization, base station on/offetc.), the terminal 100 may wake up in the coverage of a cell C3-C4resp. base station B3-B4 that is different from the original servingcell C1 or base station B1. Such a situation may occur e.g. as depictedin FIG. 1 when the terminal 100 is in the coverage of a first cell C1 atposition P1 and P2 but in the coverage of a different cell C3 and C4 atposition P3 and P4 respectively. Hence, after being connected to a firstcell C1 the terminal 100 may enter an inactive phase, such as DRX ‘OFFtime’, and may wake up from that inactive phase having lost theconnection to the first cell C1.

In such a scenario the terminal 100 would follow the followingprocedures as shown in FIG. 2a to handle radio link failure: In a firstphase downlink quality is monitored by Layer 1 and problems indicated toRRC, e.g. the number of unsuccessfully received packets is indicated bya counter N310. RRC filters Layer 1 indications and starts a timer T310after a number of out-of-sync indications indicated by counter N310. Ifno recovery within the first phase is made, a second phase is triggeredin which Layer 2 monitors random access attempts and indicates problemsto RRC. If no recovery is made within the second phase, i.e. within atime interval provided by a timer T311, the terminal 100 autonomouslygoes into RRC idle mode.

An additional timer T312 may be added. The timer 312 may be introducedto enable faster connection recovery during mobility typically with thehelp of a shorter timer length than the Radio Link Failure timer T310.T312 may be triggered if T310 is running and a measurement report istriggered for a measurement identity. The measurement report with themeasurement identity may then trigger the timer T312. Hence, thetriggering is mainly due to a measurement reporting. If the terminal 100performs a handover, re-establishment procedure, or T310 is stopped,T312 may be stopped too. The expiry of T312 may also trigger radio linkfailure or a corresponding procedure. Timer T312 may thus be triggeredwhen timer T310 is triggered or after T310 is triggered, that is to saywhen timer T310 is already running. Preferably timer T312 is configuredto expire earlier than timer T310. For example timer T312 may beconfigured to run for a shorter period of time than timer T310.

Despite the technological developments and the procedures explained inthe above, a terminal 100 with extended DRX cycles may however end upwith lengthy procedures when it wakes up in another cell C1-C4 orcoverage of another base station B1-B4. This would cause unnecessarypower consumption (e.g., in processing) and delay (e.g., in access)especially when considering that the timers may be configured muchlonger for MTC devices (e.g. due to the coverage extension for MTCdevices).

An additional or alternative condition for starting the timer T312 or anew timer, e.g. a timer T313, may be employed, e.g. in order to enablefast connection reestablishment that follows an inactive phase, such asa (long) sleep duration e.g. as present in short/extended DRX. Thisscenario is depicted in FIG. 2b . Thus for example, instead of startingthe timer T312 upon a measurement report, timer T312 may be startedbased on the duration of an inactive phase, e.g. such as the ‘OFF time’of an DRX cycle. The inactive phase may be the inactive phase of adirectly preceding DRX cycle. However, optionally more than onepreceding inactive phase may be taken into account, e.g. of more thanone preceding DRX cycle. An exemplary scenario of such a timer T312 ortimer T313 as the case may be is depicted in FIG. 2b . Further on,instead or in addition to a timer, a counter may be initiated, startedor adapted. Thus, the adaption of a parameter, such as e.g. a counter ora timer, has the benefit of power saving (on the terminal side) andreduced access delay, in particular for machine type-devices.

In a first embodiment, a new condition may be added for triggering thetimer T312 or timer T312. Timer T312 and/or timer T313 may be configuredshorter than timer T310 and triggered due to a measurement report so asto enable faster connection recovery during mobility—as explainedpreviously. With the addition of a new condition, timer T312 and/ortimer T313 may (also) be started when the terminal 100 has beenout-of-sync since the end of an inactive phase, e.g. a sleep period or a‘OFF time’, which is longer than a predefined time threshold. Startingthe timer T312 and/or timer T313 may as well be dependent on that thetimer T310 is already running. For instance, this could be the case whenthe terminal 100 wakes up from an extended sleep/DRX time toperiodically check whether there is downlink data/paging or sporadicallytransmit uplink data. Timer T312 and/or timer T313 may stop upon atleast one of the following: receiving a number N311 (maximum number) ofconsecutive in-sync indications from lower layers, triggering thehandover procedure, initiating the connection re-establishmentprocedure, and/or the expiry of timer T310. At the expiry of timer T312,and if security is not activated: the terminal 100 may go to RRC_IDLEmode, also referred to as (RRC) idle mode. Otherwise, it may initiate aconnection re-establishment procedure or to another kind of recoveryfrom radio link failure. The terminal 100 may as well go directly toRRC_idle mode.

Additionally or alternatively to the above, a new timer, e.g. a timerT313, may be introduced. In the first alternative, timer T313 startsupon the end of an inactive phase, such as an extended DRX cycle, andmay be configured to run for a shorter duration than timer T310. TimerT313 may thus be started upon a duration of an inactive phase which islonger than a predefined time threshold. This threshold may be set inadvance by the terminal vendor or may be received from a base stationB1-B4 of the cellular network. By way of the determined and/orpredefined threshold the probability of the terminal changing cells(during the inactive phase) may be taken in to account. This probabilityand thus the determined or predefined threshold may be dependent on e.g.the mobility of the terminal 100, size of an area covered by a cellC1-C4, a device category of the terminal 100 or the like. Additionallyor alternatively a QoS (Quality of Service) requirement, an applicationtype, or the like may be used.

In another embodiment timer T313 may additionally or alternatively startwhen the terminal 100 enters an inactive phase, e.g. ‘OFF time’, timerT313 may then be adapted, e.g. may be set, to run for a predefinedamount of time, e.g. defined by said predefined threshold, denoted asDRX_thr in the following; and/or timer T313 may be set to run for aperiod of time dependent on the duration of timer T310; and/or timerT313 may be set to run for a period of time dependent on the duration oftimer T312. Thus, the predefined threshold DRX_thr may be set and theduration of timer T313 may be adapted based on said threshold or basedthe duration of another timer.

Timer T313 may stop, in particular upon receiving a number ofconsecutive in-sync indications determined by counter N311, e.g. fromlower layers, upon triggering a handover procedure, upon initiating aconnection re-establishment procedure, and/or upon the expiry of timerT310 and/or timer T312. At the expiry of timer T313, and in casesecurity is not activated the terminal may be configured to go intoRRC_IDLE mode, which also may be the case at expiry of timer T310 ortimer T312. Otherwise, it initiates a connection re-establishmentprocedure.

According to a further embodiment a RRC connection reestablishmentmessage indicating the reestablishment cause may be send from theterminal 100 to a base station B1-B4. The reestablishment cause may bethat the duration of the inactive phase, such as the extended DRX or asleep time, is longer than a predefined time threshold (e.g., DRX ‘OFFtime’>DRX_thr [seconds]). This reestablishment message may be sent ifthe connection re-establishment procedure starts upon the new conditionof timer T312 or the new timer T313. The RRC connection reestablishmentmessage may include an information element e.g., an reestablishmentcause that indicates the reestablishment cause as the extended DRX or asleep time that is longer than a predefined time threshold (e.g.,DRX>DRX_thr [seconds]).

FIG. 3 shows an exemplary flow chart schematically illustrating a methodand method steps S301, S302, S303 according to an embodiment of theinvention with regard to a terminal 100. That is to say, the method asshown in the flow chart is at least partially or completely performed bythe terminal 100 or one or more components of the terminal 100. Theterminal 100 may thus be capable of detecting a radio link failurebetween it and a base station B1-B4, e.g. based on monitoring and/orevaluating the radio link.

The terminal 100 is configured to adapt in step S302 at least oneparameter (e.g. initiate a timer, set a starting condition for a timer,set a duration of a timer or initiate a counter, set a startingcondition of a counter) used in monitoring said radio link, based on aduration of an inactive phase, in which the terminal 100 is nottransmitting to and/or receiving data from the base station B1-B4 viathe radio link. The parameter may very well be the above discussed timerT312 and/or timer T313.

The one or more parameter, which may by way of example be a high layerfiltering parameter, may be used when monitoring the radio and/or inradio link failure evaluation i.e. used to evaluate and detect radiolink failure between the terminal 100 and a (serving) base station B1-B4(or (serving) eNodeB). The terminal 100 may further on be capable ofoperating in DRX mode having at least one DRX cycle. Additionally, themethod may thus comprise the step S303 of monitoring said radio linkbased on said at least one adapted parameter after adapting the at leastone parameter.

The method may further comprise the step of comparing the duration ofsaid inactive phase with a predefined threshold, and adapting said atleast one parameter based on said comparison. As mentioned earlier, theterminal 100 can adapt the parameter(s) as a function of the duration ofthe inactive phase. The duration of the inactive phase may be determinedin a step S301 by the terminal 100 itself or may even be received by abase station. The duration of the inactive phase may then be compared tosaid predefined threshold, which threshold may for instance bedetermined in said step S301 by the terminal 100 itself or may bereceived from a base station B1-B4.

The step S302 of adapting may comprise the step of initiating saidparameter based on the duration of said inactive phase.

Preferably the inactive phase is an inactive phase, conventionallydenoted as ‘OFF time’, of a discontinuous reception, DRX, cycle or adiscontinuous transmission, DTX, cycle. Thus, the method may furthercomprise the step of determining the duration of said inactive phasebased on the duration of a DRX sleep state of said DRX cycle. Preferablysaid at least one parameter corresponds to a start time, an end timeand/or a duration of said first parameter, which first parameterpreferably corresponds to a first time. Additionally, the start time,the end time and/or the duration of said first parameter, preferablysaid first timer, is adapted as a function of, e.g. the duration, saidinactive phase. However instead of a timer or additionally to a timer acounter may be used.

Optionally, the method further comprises the step of monitoringcomprises, monitoring the radio link between the terminal 100 and thebase station B1-B4 while said first timer is running.

The step of adapting may further comprise at least one of the followingsteps initiating said first timer, e.g. timer T312 or timer T313, basedon the duration of said inactive phase, initiating said first timer incase the duration of said inactive phase exceeds said predefinedthreshold, initiating said first timer in case the terminal has beenout-of-sync, e.g. after a number of out-of-sync indications, preferablyafter the end of a directly preceding inactive phase, starting saidfirst timer after said inactive phase, preferably at the end of saidinactive phase, starting said first timer at the beginning of saidinactive phase.

The method may further comprise the step of running said first timer atleast partly in parallel to a second timer.

In particular the step of adapting said first parameter, e.g. said firsttimer, may comprise adapting said first parameter to run for a shorterperiod of time than said second timer. The first timer may thus beadapted to lapse before said second timer. This may be achieved startingthe first timer at a point of time before or equal to a point of timestarting the said second timer

According to an embodiment of the method said second timer correspondsto a timer for evaluating a radio link failure. However, also the firsttimer may correspond to a timer for evaluating a radio link failureand/or monitoring said radio link.

The method may further comprise the step of evaluating a radio linkfailure based on monitoring said radio link while said first timer isrunning. This may be achieved by observing out-of-sync between theterminal and the base station in order to evaluate radio link failuredetection according to said parameter. This may be achieved by using aparameter such as a timer and/or a counter. Thus, the at least one firstand/or the at least one second parameter may be a timer, a counter or acombination thereof.

The step of determining the threshold may further comprise the step ofdetermining said threshold, e.g. out of a plurality of availablepredefined thresholds. For example only a limited amount of predefinedthresholds may be available. One of those predefined thresholds may beselected in order to serve a threshold to compare the duration of theinactive phase with said selected threshold. For example, a certainthreshold may be selected according to a device category of theterminal.

The method may additionally comprise the step of transmitting a message,e.g. containing radio link failure information, from the terminalindicating that said predefined threshold has been exceeded. Thismessage may be transmitted after the step of comparing the duration ofsaid inactive phase with said predefined threshold. The result of thiscomparison may then be included in that message.

The method may further comprise the step of initiating a connectionre-establishment procedure after the first timer has expired.

Now referring to FIG. 4, there is illustrated an exemplary structure ofan exemplary terminal 100 for performing the method of FIG. 3 and/or thedifferent previously described embodiments. As shown, the terminal 100includes a DRX module comprising means for enabling the terminal 100 tooperate in a DRX mode having at least one DRX cycle (e.g. short or longetc.); a processor comprising means for adapting the one or moreparameter (i.e. higher layer filtering parameters such as countersand/or timers) as a function of, e.g. the duration of, the inactivephase of the DRX cycle the terminal 100 is using; and a monitoringmodule comprising means for monitoring a radio link based on the one orseveral adapted parameters. The monitoring module may additionallycomprise means for evaluating radio link failure detection based on theone or several adapted parameters. The terminal 100 may further comprisea receiver unit RX adapted to receive radio signals via a radio link toone or more base station B1-B4, e.g. of a cellular network. The receiverunit RX may further be adapted to receive a configuration message (ormessages) from a base station B1-B4. Such message(s) may comprise one ormore predefined thresholds which the terminal 100 can be used to comparethe duration of one of the preceding inactive phases, e.g. of one ormore preceding DRX cycle, that is used by terminal 100. The terminal 100further includes a transmitter unit TX adapted to transmit to the basestation B1-B4 information related to radio link conditions aftermonitoring and/or evaluating the radio link, e.g. by way of themonitoring module, for example based on one or more adapted parameter.The different exemplary modules and units shown in FIG. 4 are notnecessarily separated. Furthermore the transmitter unit TX and thereceiver unit RX may also be realized in one and the same unit. Theterminal 100 is therefore not restricted and is not limited to theexemplary block diagrams shown in FIG. 4. In addition, the terminal 100may also comprise other elements and/or units not illustrated in FIG. 4.

The terminal 100 may thus be capable of monitoring a radio link betweenthe terminal 100 and a base station B1-B4, and may be configured toadapt at least one parameter, used in monitoring said radio link, basedon a duration of an inactive phase, in which the terminal is nottransmitting to and/or receiving data from the base station via theradio link. The terminal 100 may further be configured to monitor saidradio link based on said at least one adapted parameter. The terminal100 may be adapted to compare a duration of said inactive phase with apredefined threshold, e.g. by way of the determining module. Theterminal 100 may further be capable to adapt at least one parameterbased on said comparison, e.g. by way of the adapting module.

The terminal 100 may thus comprise a processor; and a memory, saidmemory containing instructions executable by said processor, wherebysaid terminal is operative to:

compare a duration of an inactive phase, in which the terminal 100 isnot transmitting to and/or receiving data from the base station B1-B4via the radio link, with a predefined threshold, and adapt at least oneparameter based on said comparison, and monitor said radio link based onsaid at least one adapted parameter.

The terminal 100 may comprise a receiver unit RX and/or transmitter unitTX transmitting and/or receiving data from said base station as the casemay be. The terminal 100 may thus be adapted to switch off the receiverunit and/or transmitter unit RX, TX during the inactive phase. This maybe achieved by said DRX module as depicted in FIG. 4.

The terminal 100 may optionally be adapted to operate in discontinuousreception, DRX, or discontinuous transmission, DTX, mode and/or todetermine the duration of said inactive phase based on the duration of aDRX or DTX sleep state, i.e. ‘OFF time’, of said DRX or DTX mode.

The at least one parameter adapted and/or deployed during monitoringsaid radio link may correspond to a first timer, which first timer ispreferably adapted as a function of said at least one inactive phase,and/or wherein said terminal is adapted to monitor the radio linkbetween the terminal and the base station while said first timer isrunning. Instead of a timer said first parameter may also be a counter.Besides a plurality of parameters may be adapted and/or employed duringmonitoring said radio link. For example, a first parameter may be atimer, as described above, and a second parameter may be counter, asdescribed above as well. For example the first timer may be the timerT312 or timer 313 as described in the above.

Additionally, the terminal 100 may configured to adapt said first timerby scaling the duration of the inactive phase, e.g. using a scalingfactor, and/or said terminal is configured to start said first timer incase said inactive phase exceeds said predefined threshold, and/or saidterminal is configured to start said first timer after a precedinginactive phase, preferably at the end of a directly preceding inactivephase, and/or said terminal is configured to start said first timer ifthe terminal 100 has been out-of-sync, e.g. after a number ofout-of-sync indications, preferably after the end of a directlypreceding inactive phase, and/or said terminal 100 is configured tostart said first timer at the beginning of said inactive phase.

Optionally, said terminal 100 is configured to run said first timer atleast for a time in parallel to a second timer, wherein preferably saidfirst timer is initialized to run for a shorter period of time than saidsecond timer, wherein in particular said second timer corresponds to atimer for evaluating a radio link failure after a number of out-of-syncindications.

The terminal 100 may also be configured to evaluate a radio link failurebased on monitoring said radio link while said first timer is running,and/or said terminal is configured to observe out-of-sync between theterminal and the base station in order to evaluate radio link failuredetection according to said parameter.

Further on, the terminal 100 may be configured to determine saidpredefined threshold, e.g. out of a plurality of available predefinedthresholds, according to a device class of the terminal 100, and/or saidterminal is configured to transmit a message, e.g. containing radio linkfailure information, from the terminal that indicates that saidpredefined threshold has been exceeded, and/or said terminal isconfigured to initiate a connection re-establishment procedure after thefirst timer has expired.

Now referring to FIG. 5, there is illustrated a flowchart of a methodand method steps S501, S502, performed by a base station (e.g. eNodeB oreNB) B1-B4 for enabling a terminal 100 to adapt a parameter, monitor aradio link and/or detect radio link failure between the terminal and thebase station. The terminal 100 is capable of operating in DRX modehaving at least one DRX cycle. As shown in FIG. 5, the main stepsperformed in the base station comprise: transmitting (or signaling) athreshold to the terminal, in a step S502, on the basis of which one orseveral parameters are adapted, e.g. as a function of the threshold,and/or for comparing said predefined threshold with the duration of aninactive phase, e.g. of the current DRX cycle. The one or severalparameters (i.e. high layer filtering parameters such as timers andcounters) may be used when monitoring said radio link or in radio linkfailure evaluation.

Optionally the base station B1-B4 may receive from the terminal 100information relating to a reporting on radio link conditions, after thatthe terminal 100 has evaluated the radio link failure (RLF) detectionbased on the adapted parameter(s).

Thus, a method according to the present invention may be used in a basestation B1-B4 and enabling a terminal 100 to monitor a radio linkbetween the terminal 100 and said base station B1-B4, the methodcomprising: transmitting a message to the terminal setting a predefinedthreshold for comparing said predefined threshold with a duration of aninactive phase, during which inactive phase the terminal is nottransmitting to and/or receiving data from the base station via theradio link.

Said threshold may be determined by the base station B1-B4 in a stepS501. As already mentioned the area covered by a cell or base stationand/or a device category or the like may be taken into account whendetermining said threshold.

Referring to FIG. 6, exemplary structures of a base station BN (e.g.eNodeB or eNB) for enabling a terminal 100 to adapt a parameter, monitora radio link and/or detect radio link failure between the terminal 100and the base station BN are illustrated. The terminal 100 may beconfigured to adapt at least one parameter used to monitor a radio link,evaluate and detect radio link failure between it and the base stationBN. As mentioned before, the terminal 100 may be configured to operatein DRX mode having at least one DRX cycle (long or short). As shown inFIG. 6, the base station BN includes a transmitter unit TX comprisingtransmitting means that is configured to transmit (or signal) athreshold to the terminal. The terminal 100 can then use the receivedthreshold to adapt the one or several parameters as a function of thethreshold and/or as a function of the length or duration or period ofthe inactive phase of a current DRX cycle. Additionally the terminal 100may be adapted to compare the received threshold with the duration of aninactive phase. The threshold may e.g. be sent to the terminal 100 in aconfiguration message.

The base station BN further includes a receiver unit RX comprisingreceiving means configured to receive, after evaluation by the terminal100 of the radio link based on the adapted parameter(s), informationrelating to a reporting on radio link conditions. Note that thedifferent exemplary units shown in FIG. 6 are not necessarily separated.The base station BN may also include a processor comprising processingmeans for e.g. processing information received/transmitted from/to oneor several terminals. Although the base station may comprise additionalelements and/or units such as integrated circuits and discretecomponents which are known by a person skilled in the art, theseadditional elements and units are not illustrated in FIG. 6.

Thus, an embodiment comprises a base station BN for enabling a terminal100 to monitor a radio link between the terminal 100 and said basestation BN, the terminal 100 comprising an inactive phase, in which theterminal 100 is not transmitting to and/or receiving data from the basestation BN via the radio link, said base station BN being adapted totransmit a first message to the terminal setting a predefined thresholdfor comparing said predefined threshold with a duration of said inactivephase.

Optionally, the base station BN is adapted to transmit a second messageto the terminal 100 setting a duration of said inactive phase. Furtheron, said base station may be adapted to determine a duration of saidinactive phase and/or said threshold based on a device category of saidterminal 100. On or more of the base station according to FIG. 1 may beembodied in a way corresponding to the exemplary base station BN of FIG.6.

Now referring to FIG. 7, a flow chart diagram for implementing a furtherembodiment is schematically illustrated.

In case a radio problem has been detected in a step S701 the duration ofa previous inactive phase is compared with a predefined threshold in astep S702. The radio problem detection may be based on a number ofunsuccessful decodings of received data packets, e.g. accounted for by acounter N310. If this number is exceeded a radio link failure isdetected. Subsequently, the duration of the inactive phase is comparedwith said predefined threshold. In case the inactive phase is longerthan the threshold, i.e. exceeds said threshold, a timer, e.g. timerT313, is started. Thus, in the embodiment of FIG. 7 the timer T313 isstarted after the radio problem detection in a step S703. However, thetimer T313 may be started directly after the end of the inactive phase,i.e. after switching of the receiver unit RX(and receiving datapackets). Alternatively, the timer T313 may be started at the beginningof the inactive phase or after a recovery interval, cf. timer T310 inFIG. 1. Thus, step S702 may be executed e.g. after waking up from aninactive phase such as a (long) DRX cycle, in particular of a mobile MTCdevices.).

After timer T313 has been started it is examined whether one or morerecovery or abortion conditions are fulfilled in a step S704. Suchconditions may be by way of example a number of in-sync indications, forwhich e.g. a counter like N311, can be used; a handover or connectionre-establishment command is received by the terminal; another timer,e.g. timer T310 or timer T312, expired in the meantime. Accordingly,timer T313 may then be stopped in a step S706.

If during the runtime of timer T313 no recovery or abortion has beenachieved the terminal may initiate a connection re-establishmentprocedure or go to RRC_IDLE mode. This may include monitoring theruntime and expiration of the timer T313 in a step S705. Hence, aftertimer T313 expired the terminal may initiate a connectionre-establishment procedure in a step S708 or got RRC_IDLE mode in a stepS709. Additionally, after expiration of timer T313 it may be checkedwhether (AS) security or another type of secure communication has beenactive in a step S707. For example, if security has been activated aconnection re-establishment procedure may be initiated whereas in casesecurity has not been activated the terminal may go into RRC_IDLE statedirectly.

By setting the runtime of timer T313 to a shorter duration than runtimeof timer T310 and/or T311 or by setting the timer T313 to expire earlierthan timer T310 or timer T311 radio link failure may detected fasterthan previously possible. In the flowchart diagram of FIG. 7 timer T310may be started upon detection of a radio problem, whereas timer T311 maybe started after expiry of timer T310 or may be started together withtimer T313 or even after timer T313 has been started. However, insteadof a new timer T313 a timer already present in the 3GPP specification,e.g. timer T312, may be used in order to monitor said radio link.

FIG. 8 shows a plot of battery runtime of a terminal as a function ofDRX cycle length, in seconds (s), in the case that the terminal leavesthe coverage area of a cell every 30 minutes. The plot has been made fortimer settings of 2000 ms for T310 and 100 ms for T312. The dotted linescorrespond to the battery runtime for conventional radio link monitoringwhich is done (only) based on timer T310 which is started upon detectionof a radio link problem and/or end of an inactive phase, whereas thesolid lines correspond to a radio link monitoring in which a timeradapted according to the length of the inactive phase is employed. Thetimer is denoted as T312 in this embodiment but may however be the timerT313 as described in the above. The different lines correspond todifferent inter-arrival times, as indicated in FIG. 8, of an uplinkpayload of 125 Byte, and based on that the terminal listens to paging ofa base station, e.g. during a DRX ‘ON time’. The same inter-arrivaltimes have also been used for the conventional radio link monitoring(dotted lines).

Timer T312 is in this case started at the same point in time as timerT310 and is set to run for a shorter duration than timer T310, asindicated above. However, timer T312 is only started in case the DRX‘OFF time’ exceeds a predefined threshold. The combination of thepredefined threshold and the reduced runtime of timer T312 yields asignificant reduction of power consumption and thus in case of a batterypowered terminal 100 to an extended battery life.

The above described embodiments can be realized in many ways. As anexample, suitable processors in associations with software and hardwaremeans may be used to implement the method claims related to the terminaland the method claims related to the base station. For example, oneembodiment includes a computer-readable medium having instructionsstored thereon that are executable by a terminal. The instructions whenexecuted perform the method steps related to the terminal as set forthin the claims.

Furthermore, the exemplary embodiments of the present invention may beimplemented in any type of wireless communications system that employsDRX modes of operation. By way of example, the exemplary embodiments ofthe present invention may be implemented in a non-limiting generalcontext in relation to a 4G LTE concept and/or UMTS and/or WiMAX and/orHSPA and/or HSDPA (high speed downlink packet access) and/or HSUPA.

While the invention has been described in terms of several preferredembodiments, it is contemplated that alternatives, modifications,permutations and equivalents thereof will become apparent to thoseskilled in the art upon reading of the specifications and study of thedrawings. It is therefore intended that the following appended claimsinclude such alternatives, modifications, permutations and equivalentsas fall within the scope of the embodiments of the present invention.

The invention claimed is:
 1. A method for monitoring a radio linkbetween a base station and a terminal in a wireless communicationsystem, comprising: setting a start time of a first timer for radio linkfailure recovery, which is used in monitoring the radio link, based on aduration of an inactive phase in which the terminal is not transmittingto and/or receiving data from the base station via the radio link. 2.The method of claim 1, further comprising: monitoring the radio linkbased on the start time of the first timer for radio link failurerecovery.
 3. The method of claim 1, further comprising: comparing theduration of the inactive phase with a predefined threshold, whereinsetting the start time of the first timer is based on the comparison. 4.The method of claim 1, wherein the inactive phase is an inactive phaseof a discontinuous reception, DRX, cycle or a discontinuoustransmission, DTX, cycle.
 5. The method of claim 1, further comprising:determining the duration of the inactive phase based on the duration ofa DRX sleep state of the DRX cycle.
 6. The method of claim 1, whereinthe start time of the first timer is adapted as a function of theinactive phase.
 7. The method of claim 1, wherein monitoring the radiolink comprises, monitoring the radio link between the terminal and thebase station while the first timer is running.
 8. The method of claim 1,wherein setting the start time of the first timer comprises initiatingthe first timer in case the duration of the inactive phase exceeds thepredefined threshold.
 9. The method of claim 1, wherein setting thestart time of the first timer comprises initiating the first timer inresponse to the terminal being out-of-sync after a number of out-of-syncindications, and after the end of a directly preceding inactive phase.10. The method of claim 1, wherein setting the start time of the firsttimer comprises starting the first timer after the inactive phase, andat the end of the inactive phase.
 11. The method of claim 10, whereinthe second timer corresponds to a timer for evaluating a radio linkfailure.
 12. The method of claim 1, wherein setting the start time ofthe first timer comprises starting the first timer at the beginning ofthe inactive phase.
 13. The method of claim 1, further comprising:running the first timer at least partly in parallel to a second timer.14. The method of claim 13, further comprising: adapting the first timerto run for a shorter period of time than the second timer.
 15. Themethod of claim 14, further comprising: adapting the first timer tolapse before the second timer.
 16. The method of claim 1, furthercomprising: evaluating a radio link failure based on monitoring theradio link while the first timer is running.
 17. The method of claim 1,further comprising: observing out-of-sync between the terminal and thebase station in order to evaluate radio link failure detection accordingto the parameter.
 18. The method of claim 1, further comprising:determining the predefined threshold, out of a plurality of availablepredefined thresholds, according to a device category of the terminal.19. The method of claim 1, further comprising: transmitting a message,including radio link failure information, from the terminal indicatingthat the predefined threshold has been exceeded.
 20. The method of claim1, further comprising: initiating a connection re-establishmentprocedure after the first timer has expired.
 21. A terminal capable ofmonitoring a radio link between the terminal and a base station, theterminal comprising: a processor; and memory having instructions storedtherein that are executable by the processor to cause the terminal toperform operations, the operations comprising: setting a start time of afirst timer for radio link failure recovery, which is used in monitoringthe radio link, based on a duration of an inactive phase in which theterminal is not transmitting to and/or receiving data from the basestation via the radio link.
 22. The terminal of claim 21, the operationsfurther comprising: monitoring the radio link based on the start time ofthe first timer for radio link failure recovery.
 23. The terminal ofclaim 22, the operations further comprising: determining the predefinedthreshold, out of a plurality of available predefined thresholds,according to a device class of the terminal; transmitting a message,including radio link failure information, from the terminal thatindicates that the predefined threshold has been exceeded; andinitiating a connection re-establishment procedure after the first timerhas expired.
 24. The terminal of claim 21, the operations furthercomprising: comparing a duration of the inactive phase with a predefinedthreshold, wherein setting the start time of the first timer comprisessetting the start time of the first timer based on the comparison. 25.The terminal of claim 21, further comprising: a receiver unit configuredto receive data from the base station; and/or a transmitter unitconfigured to transmit data from the base station.
 26. The terminal ofclaim 25, the operations further comprising: switching off the receiverunit and/or the transmitter unit during the inactive phase.
 27. Theterminal of claim 21, the operations further comprising: operating in adiscontinuous reception (“DRX”) mode or a discontinuous transmission(“DTX”) mode; and determining the duration of the inactive phase basedon the duration of a DRX or a DTX sleep state of the DRX mode or the DTXmode.
 28. The terminal of claim 21, the operations further comprising:monitoring the radio link between the terminal and the base stationwhile the first timer is running.
 29. The terminal of claim 21, theoperations further comprising: adapting the first timer by scaling theduration of the inactive phase using a scaling factor; starting thefirst timer in response to the inactive phase exceeding the predefinedthreshold; starting the first timer after a preceding inactive phase,and at the end of a directly preceding inactive phase; starting thefirst timer in response to determining that the terminal is out-of-syncand after the end of a directly preceding inactive phase; and startingthe first timer at the beginning of the inactive phase.
 30. The terminalof claim 29, the operations further comprising: running the first timerat least for a time in parallel to a second timer; and initializing thefirst timer to run for a shorter period of time than the second timer,wherein the second timer corresponds to a timer for evaluating a radiolink failure after a number of out-of-sync indications.
 31. The terminalof claim 21, the operations further comprising: evaluating a radio linkfailure based on monitoring the radio link while the first timer isrunning; and observing out-of-sync between the terminal and the basestation in order to evaluate radio link failure detection according tothe parameter.
 32. A non-transitory computer-readable medium havinginstructions stored therein that are executable by a processor of aterminal to cause the terminal to perform operations, the operationscomprising: setting a start time of a first timer for radio link failurerecovery, which is used in monitoring the radio link, based on aduration of an inactive phase in which the terminal is not transmittingto and/or receiving data from the base station via the radio link. 33.The non-transitory computer-readable medium of claim 32, wherein settingthe start time of the first comprises starting the first timer at thebeginning of the inactive phase.